Cooling unit, and apparatus for separating air by means of cryogenic distillation including such cooling unit

ABSTRACT

The invention relates to a cooling unit consisting of an exchange line capable of heating nitrogen originating from the system of columns by exchanging heat with the air to be cooled for the system of columns, and a cooling tower for the heat- and mass-exchange between the water to be cooled sent to the top of the tower and the nitrogen originating from a system of air distillation columns, the lower portion of the tower including an inlet connected to a nitrogen pipe, and the nitrogen pipe being connected to at least one exchanger body of the exchange line, which is capable of heating the nitrogen originating from the system of columns by exchanging heat with the air to be cooled for the system of columns, wherein the tower is arranged above at least one portion of the exchange line.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a §371 of International PCT Application PCT/FR2011/051670, filed Jul. 12, 2011, which claims the benefit of FR1055722, filed Jul. 13, 2010, both of which are herein incorporated by reference in their entireties.

TECHNICAL FIELD OF THE INVENTION

The present invention relates to a cooling unit and to an apparatus for separating air by air distillation comprising such a cooling unit.

BACKGROUND

The “Industrial Gas Handbook” by Frank Kerry, CRC Press, pages 112 to 113 explains how to use a cooling tower to cool the air intended for air separation, in a distillation system, by direct contact with water in a first tower. The air is then conveyed to a purification system where it is dried and purified in terms of carbon dioxide. The water used for cooling obviously becomes heated in the first tower. In order to cool it and thus be able to recirculate it to the first tower, the water is cooled in a second tower by direct contact with nitrogen coming from the air distillation system. Upstream of the second tower, the nitrogen is heated up in the exchange line where the air that is to be distilled is cooled down. As Kerry points out, this flow of nitrogen may constitute a considerable percentage of the distilled air.

EP-A-1666822 shows the first and second tower positioned on the ground, the second tower being near the outlet of the main exchange line.

Pumps used for transferring the ice-water obtained in the second tower to the first tower are generally installed on the ground beside the second tower.

This second tower may be made of steel or of concrete, with a round or square cross section.

SUMMARY OF THE INVENTION

In the case of the method producing low-pressure nitrogen, for example an air separation apparatus that is supposed to supply oxygen for oxycombustion, the pressure drops in the line for residual nitrogen leaving the exchange line toward this second tower are critical because it is these that set the pressure of the low-pressure column (and therefore of the air compressor) which is connected only to the second tower where exchange of heat between the nitrogen and the water takes place.

The tower, of round or square cross section, will be installed at a height, for example on the roof of the main exchange line so as to allow the residual nitrogen line to enter the tower directly with no pipe elbows and with a minimum length of piping, both these features generating pressure drops.

This tower may be made of steel, of concrete or of plastic.

The tower will preferably be supported by a continuation of the structure of the outer casing in which the exchange line is installed or by any other suitable support means.

By using the present invention, it is possible to reduce the pressure drops by 3 mbar, and therefore to reduce the pressure of the low-pressure column by 3 mbar and that of the medium-pressure column by 4 mbar. Hence the pressure of the air is likewise reduced and the electric power consumption of the air compressor drops by 0.1%.

This reduction in pressure is the result of the elimination of three pipe elbows in the piping conveying the nitrogen from the exchange line to the cooling tower by comparison with the prior art in which the tower is placed at ground level.

One object of the invention is to provide a cooling unit consisting of an exchange line capable of heating up the nitrogen coming from a system of columns by exchange of heat with air that is to be cooled that is bound for the system of columns and a cooling tower allowing exchange of heat and mass between the water that is to be cooled, sent in at the top of the tower and nitrogen coming from a system of air distillation columns, the lower part of the tower comprising an inlet connected to a nitrogen pipe and the nitrogen pipe being connected to at least one exchanger body of the exchange line, capable of heating up the nitrogen coming from the system of columns by exchange of heat with air that is to be cooled that is bound for the system of columns characterized in that the tower is positioned above at least part of the exchange line.

According to other optional features:

-   -   the tower is supported on at least part of the exchange line;     -   the tower is supported by a structure mounted on at least part         of the exchange line;     -   the lowermost point of the tower is above the exchanger body or         bodies;     -   the nitrogen pipe is connected to a point above the tank of the         cooling tower;     -   the unit comprises two exchange lines each one comprising         several exchange bodies, the two exchange lines preferably         having substantially the same height;     -   the tower is supported by a structure mounted on the two         exchange lines;     -   the tower is positioned above a space between the two exchange         lines;     -   at least one air inlet pipe connected to the two exchange lines         passes through the space underneath the tower;     -   the nitrogen pipe is connected to the upper part of the         exchanger body;     -   the nitrogen pipe is arranged in such a way that the nitrogen         reaches the tower without being conveyed downward;     -   the nitrogen pipe comprises at most one single pipe elbow,         preferably no pipe elbow, between the exchanger body and the         nitrogen pipe;     -   the system of columns comprises a medium-pressure column and a         low-pressure column, and the low-pressure column is connected to         the body of the exchange line to supply it with nitrogen.

Another object of the invention is to provide an apparatus for separating air by cryogenic distillation, comprising a unit as claimed in one of claims 1 to 12, a system of columns, a pipe conveying air to the exchange line, a pipe conveying air from the exchange line and a pipe conveying air from the exchange line to the system of columns, the nitrogen pipe being connected to the system of columns.

Another object of the invention is to provide a method for separating air by cryogenic distillation using a unit as claimed in one of claims 1 to 12, in which air is cooled in the tower and in the exchange line, separated in a system of columns, the nitrogen is sent from the system of columns to the exchange line and from the exchange line to the tower.

For preference, the pressure drop in the nitrogen pipe between the outlet of the exchanger body and the inlet of the tower is less than 7 mbar, preferably less than 6 mbar.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other features, aspects, and advantages of the present invention will become better understood with regard to the following description, claims, and accompanying drawings. It is to be noted, however, that the drawings illustrate only several embodiments of the invention and are therefore not to be considered limiting of the invention's scope as it can admit to other equally effective embodiments.

FIG. 1 represents an apparatus in accordance with an embodiment of the invention.

DETAILED DESCRIPTION

The invention will be described in greater detail with reference to the figure which depicts a unit according to an embodiment of the invention incorporated into a device for separating air by cryogenic distillation.

The cooling unit comprises a tower 1, two low-pressure exchange lines 3A, 3B, and one high-pressure exchange line 5. The air separation apparatus additionally comprises air turbines 7, distillation columns 9, 11 and a set of piping and valves.

The air is cooled in a tower (not illustrated) by direct contact with water, purified in a purification device, cooled in the exchange lines 3A, 3B, expanded through at least one turbine 7 and sent to a column 9 to be separated. Fluids produced in the column 9 are sent to the column 11, which operates at a lower pressure than the column 9. The nitrogen produced, coming from the column 11, is heated up in the exchange lines 3A, 3B and conveyed to the cooling tower 1 where it cools the water intended for cooling the air.

The exchange lines 3A, 3B are low-pressure fluid exchangers and are separated by a space. Each exchange line comprises a certain number of bodies (in this instance eight) which receive air to be cooled and nitrogen to be heated.

The heated-up nitrogen is collected in pipes 15 which emerge a few meters above the bottom of the tower 1. The nitrogen pipe 15 is higher up than the other pipes and is therefore easier to connect to the tower 1. The pressure drop on the nitrogen pipe 15 between the exchange body and the tower is less than 7 mbar, preferably less than 6 mbar.

The tower 1 is supported by a structure 13 which rests on the ends of the two exchange lines 3A, 3B.

The water cooled in the tower is used to cool the air upstream of the purification process.

Where there is just one exchange line, the structure 13 will rest on the ground or on some other element.

The water inlet and outlet pipes have not been illustrated in the figure.

While the invention has been described in conjunction with specific embodiments thereof, it is evident that many alternatives, modifications, and variations will be apparent to those skilled in the art in light of the foregoing description. Accordingly, it is intended to embrace all such alternatives, modifications, and variations as fall within the spirit and broad scope of the appended claims. The present invention may suitably comprise, consist or consist essentially of the elements disclosed and may be practiced in the absence of an element not disclosed. Furthermore, if there is language referring to order, such as first and second, it should be understood in an exemplary sense and not in a limiting sense. For example, it can be recognized by those skilled in the art that certain steps can be combined into a single step.

The singular forms “a”, “an” and “the” include plural referents, unless the context clearly dictates otherwise.

“Comprising” in a claim is an open transitional term which means the subsequently identified claim elements are a nonexclusive listing (i.e., anything else may be additionally included and remain within the scope of “comprising”). “Comprising” as used herein may be replaced by the more limited transitional terms “consisting essentially of” and “consisting of” unless otherwise indicated herein.

“Providing” in a claim is defind to mean furnishing, supplying, making available, or preparing something. The step may be performed by any actor in the absence of express language in the claim to the contrary a range is expressed, it is to be understood that another embodiment is from the one.

Optional or optionally means that the subsequently described event or circumstances may or may not occur. The description includes instances where the event or circumstance occurs and instances where it does not occur.

Ranges may be expressed herein as from about one particular value, and/or to about another particular value. When such particular value and/or to the other particular value, along with all combinations within said range.

All references identified herein are each hereby incorporated by reference into this application in their entireties, as well as for the specific information for which each is cited. 

1-15. (canceled)
 16. A cooling unit comprising of an exchange line capable of heating up the nitrogen coming from a system of columns by exchange of heat with air that is to be cooled that is bound for the system of columns and a cooling tower allowing exchange of heat and mass between the water that is to be cooled, sent in at the top of the tower and nitrogen coming from a system of air distillation columns, the lower part of the tower comprising an inlet connected to a nitrogen pipe and the nitrogen pipe being connected to at least one exchanger body of the exchange line, wherein the tower is positioned above at least part of the exchange line.
 17. The cooling unit as claimed in claim 16, in which the cooling tower is supported on at least part of the exchange line.
 18. The cooling unit as claimed in claim 16, in which the cooling tower is supported by a structure mounted on at least part of the exchange line.
 19. The cooling unit as claimed in claim 16, in which the lowermost point of the cooling tower is above the exchanger body or bodies.
 20. The cooling unit as claimed in claim 16, in which the nitrogen pipe is connected to a point above the tank of the cooling tower.
 21. The cooling unit as claimed in claim 16, comprising two exchange lines each one comprising several exchange bodies, the two exchange lines preferably having substantially the same height.
 22. The cooling unit as claimed in claim 21, wherein the cooling tower is supported by a structure mounted on the two exchange lines.
 23. The cooling unit as claimed in claim 21, wherein the cooling tower is positioned above a space between the two exchange lines.
 24. The cooling unit as claimed in claim 23, in which at least one air inlet pipe connected to the two exchange lines passes through the space underneath the tower.
 25. The cooling unit as claimed in claim 16, in which the nitrogen pipe is connected to the upper part of the exchanger body.
 26. The cooling unit as claimed in claim 25, in which the nitrogen pipe is arranged in such a way that the nitrogen reaches the tower without being conveyed downward.
 27. The cooling unit as claimed in claim 25, in which the nitrogen pipe comprises at most one single pipe elbow between the exchanger body and the nitrogen pipe.
 28. A device for separating air by cryogenic distillation, comprising the cooling unit as claimed in claim 16, a system of columns, a pipe conveying air to the exchange line, a pipe conveying air from the exchange line and a pipe conveying air from the exchange line to the system of columns, the nitrogen pipe being connected to the system of columns.
 29. A method for separating air by cryogenic distillation using the cooling unit as claimed in claim 16, in which air is cooled in the tower and in the exchange line, separated in a system of columns, the nitrogen is sent from the system of columns to the exchange line and from the exchange line to the tower.
 30. The method as claimed in claim 29, in which the pressure drop in the nitrogen pipe between the outlet of the exchanger body and the inlet of the tower is less than 7 mbar, preferably less than 6 mbar. 